The Nervous System

EQ How does the nervous system work to control and maintain bodily functions and activities?

GPS SAP3. Students will assess the integration and coordination of body functions and their dependence on the endocrine and nervous systems to regulate physiological activities. a. Interpret interactions among hormones, senses, and nerves which make possible the coordination of functions of the body. b. Investigate the physiology of electrochemical impulses and neural integration and trace the pathway of an impulse, relating biochemical changes involved in the conduction of the impulse. c. Describe how the body perceives internal and external stimuli and responds to maintain a stable internal environment, as it relates to biofeedback.

Functions of the Nervous System 1.Sensory input—gathering information –To monitor changes occurring inside & outside the body –Changes = stimuli 2.Integration –To process and interpret sensory input & decide if action is needed

Functions of the Nervous System 3.Motor output –A response to integrated stimuli –The response activates muscles or glands

Functions of the Nervous System Figure 7.1

Structural Classification of the Nervous System Central nervous system (CNS) –Brain –Spinal cord Peripheral nervous system (PNS) –Nerves outside the brain and spinal cord Spinal nerves Cranial nerves

Functional Classification of the Peripheral Nervous System Sensory (afferent) division –Nerve fibers that carry information to the central nervous system –Input Cutaneous (skin) sense organs Mechanoreceptors- detect somatic/ body stimulation Proprioceptors—detect stretch or tension NociceptorsNociceptors --detect pain & temp. changes. Nociceptors Motor (efferent) division –Nerve fibers that carry impulses away from the central nervous system –output

Organization of the Nervous System Figure 7.2

Functional Classification of the Peripheral Nervous System Motor (efferent) division (continued) –Two subdivisions Somatic nervous system = voluntary Autonomic nervous system = involuntary

Support Cells Support Cells Support cells in the CNS are grouped together as “neuroglia” Function: to support, insulate, and protect neurons (9x more numerous than neurons)

Support Cells Astrocytes –Abundant, star- shaped cells –Brace neurons –Form barrier between capillaries and neurons –Control the chemical environment of the brain

Support Cells Microglia –Spiderlike phagocytes Phagocytes (white- blood cells that fight infections) –Dispose of debris

Support Cells Ependymal cells –Line cavities of the brain and spinal cord –Circulate cerebrospinal fluid (CSF)

Support Cells Oligodendrocytes –Wrap around nerve fibers in the central nervous system –Produce myelin sheaths

Support Cells Support Cells Satellite cells –Protect neuron cell bodies Schwann cells –Form myelin sheath in jelly roll–like fashion –in the peripheral nervous system Myelin sheath— whitish, fatty material covering axons Nodes of Ranvier — gaps in myelin sheath along the axon; allows for quick transmission of electrical impulses.

Neurons Neurons = nerve cells –large, complex cells made of cell body & extensions or processes (Axons/ dendrites) –Cells specialized to transmit messages –Mature neurons don’t replace themselves. –Major regions of neurons Cell body—nucleus & metabolic center of the cell Processes—fibers that extend from the cell body

Neurons Cell body –Nissl substance Specialized rough endoplasmic reticulum –Neurofibrils Intermediate cytoskeleton Maintains cell shape

Neurons Cell body –Nucleus –Large nucleolus Processes outside the cell body –Dendrites—conduct impulses toward the cell body –Axons—conduct impulses away from the cell body

Neurons Axons end in axonal terminals Axonal terminals contain vesicles w/ neurotransmitters (NT) Axonal terminals are separated from the next neuron by a gap –Synaptic cleft—gap between adjacent neurons –Synapse—junction btwn nerves

Neuron Cell Body Location Most neuron cell bodies are found in the CNS –Gray matter—cell bodies & unmyelinated fibers –Nuclei—clusters of cell bodies w/in the white matter of the CNS Ganglia—collections of cell bodies outside the CNS

Functional Classification of Neurons 1. Sensory (afferent) neurons: –Carry impulses from the sensory receptors to the CNS Cutaneous (skin) sense organs Mechanoreceptors- detect somatic/ body stimulation Proprioceptors—detect stretch or tension NociceptorsNociceptors --detect pain & temp. changes. Nociceptors 2. Motor (efferent) neurons: –Carry impulses from the CNS to viscera, muscles, or glands

Functional Classification of Neurons Figure 7.7

Functional Classification of Neurons 3. Interneurons (association neurons) –Found in neural pathways in the CNS –Connect sensory and motor neurons

Neuron Classification Figure 7.6

Figure 7.8a Structural Classification of Neurons 1. Multipolar neurons—many extensions from the cell body

Structural Classification of Neurons 2. Bipolar neurons—one axon & one dendrite Figure 7.8b

Structural Classification of Neurons 3. Unipolar neurons—have a short single process leaving the cell body Figure 7.8c

Functional Properties of Neurons 1. Irritability –Ability to respond to stimuli 2. Conductivity –Ability to transmit an impulse

Nerve Impulses Resting neuron –The plasma membrane at rest is polarized –Fewer positive ions are inside the cell than outside the cell Depolarization –A stimulus depolarizes the neuron’s membrane –A depolarized membrane allows sodium (Na+) to flow inside the membrane The exchange of ions initiates an action potential (AP) in the neuron

Nerve Impulses Figure 7.9a–b

Nerve Impulses Action potential –If the action potential (nerve impulse) starts, it is propagated (travels) over the entire axon –Impulses travel faster when fibers have a myelin sheath (for insulation)

Nerve Impulses Repolarization –Potassium ions rush out of the neuron after sodium ions rush in, which repolarizes the membrane –The sodium-potassium pump, using ATP, restores the original configuration

Transmission of a Signal at Synapses Impulses are able to cross the synapse to another nerve –NT (chemicals) is released from a nerve’s axon terminal –The dendrite of the next neuron has receptors that are stimulated by the NT –An AP is started in the dendrite Axon terminal Vesicles Synaptic cleft Action potential arrives Synapse Axon of transmitting neuron Receiving neuron Neurotrans- mitter is re- leased into synaptic cleft Neurotrans- mitter binds to receptor on receiving neuron’s membrane Vesicle fuses with plasma membrane Synaptic cleft Neurotransmitter molecules Ion channels Receiving neuron Transmitting neuron Receptor Neurotransmitter Na + Neurotransmitter broken down and released Ion channel opensIon channel closes